In the field of appliances such as clothes washing and dishwashing machines, it is common to employ one or more pilot operated water supply or fill valves which are actuated by one or more electrical solenoids. For example, dual inlet solenoid actuated control valves of the general type disclosed in U.S. Pat. No. 2,708,092, are used in automatic clothes washing machines, and single inlet solenoid actuated fill valves of the general type disclosed in U.S. Pat. No. 3,396,848, are commonly used in automatic dishwashing machines. The construction and operation of this particular form of solenoid operated water inlet or fill valve is well known in the art and does not require further discussion.
It has been determined that the solenoid actuator on such a pilot operated valve, produces an undesirable magnetic attraction of microscopic ferrous particles within the water supply, and an accumulation of these particles either on the spring biased metal armature or on the tube supporting the armature, sometimes causes sticking of the armature and prevents proper operation of the valve. In addition, the construction of the solenoid and the magnetically attractable armature and its enclosure add significantly to the cost of the valve.
In the construction of gas fuel control valves, it is known to provide for direct actuation of the valve member with the use of a bimetallic element surrounded by an electrical heating coil. For example, U.S. Pat. Nos. 3,346,231 and 3,513,880 each disclose such a valve construction. It has also been proposed to employ similar bimetallic elements and surrounding electrical heating coils in a pilot operated diaphragm valve such as the modulating valve disclosed in U.S. Pat. No. 3,643,913. In this valve structure, a set of bimetallic blades are alternately heated and cooled in response to the temperature of the fluid flowing through the valve for modulating the flow by the pilot operated flexible diaphragm.